The present invention relates to touchscreens and other electrographic sensors. An electrographic sensor is a device for determining the co-ordinates of an event, generally in a two-dimensional system, or for inputting such co-ordinates into, for example, a computer.
Such devices in the form of touchscreens have become widely used for inputting information into computers, as a means of operating cash dispensers, sales tills, ticketing machines, computer games and medical and industrial instrumentation. They have many advantages including speed and ease of use, small size, reliability, and accuracy.
A touchscreen will usually be used in conjunction with some form of display such as a cathode ray tube or a liquid crystal screen. The touchscreen is placed over such a display and can indicate to a computer controlling the display which icon or other element of the display has been selected by the user.
Various types of touchscreen have been produced, each with its own advantages and disadvantages. For example, touchscreens may make use of capacitance, surface acoustic waves, or resistance. It is with the last of these possibilities that I am now concerned.
Resistive touchscreens employ transparent layers of a resistive material which come into contact with one another when the screen is touched. This contact completes a circuit, the resistance of which depending on the position where the contact was made. As a result, the magnitude of the output from the touchscreen will depend on the position of the touch.
Touchscreens themselves are used in conjunction with a controller which applies the desired voltages to the various resistive layers, and also passes the output of the screen, generally after digitising it, to the computer or other device to be controlled. Two main types of resistive touchscreen exist, the so-called five-wire and four-wire screens, and each type has hitherto required its own type of controller.
In order to explain this need for a particular type of controller, the two forms of screen will be described in more detail.
Four-wire touchscreens are widely available but they have the disadvantage of a shorter life than five-wire screens. Typically a four-wire screen will be rated to survive one million touches, whereas a five-wire screen will be rated to survive, say, fifteen million or more touches. This difference arises because in the case of a four-wire screen the resistance across the surface of the top, deformable, layer is critical. This resistance will vary slightly as the screen degrades through use. In the case of a five-wire screen the top, deformable, layer must remain conductive, but its precise resistance is not important. As a result, the screen will continue to function unless the screen becomes so damaged that all conductive pathways are lost.
A four-wire screen consists of two transparent, resistive layers separated by a grid of minute dots. The lower layer may be rigid, but the upper layer will be flexible so that when the screen is touched the two layers come into contact between adjacent dots where the screen is touched. The lower layer may be provided with electrodes running along its left and right edges (for example). When a potential difference is applied between those electrodes a voltage gradient will be produced from left to right. A voltage picked up by contacting this layer will therefore have a magnitude that depends on the position of contact. In this example the voltage gradient extends from left to right and therefore the voltage picked up will provide an X-co-ordinate of position. In this example, the upper layer will have electrodes along its top and bottom edges (picture the layers in the vertical plane in front of you), and analogously a voltage difference applied between those electrodes will give rise to an output whose magnitude depends on the Y-co-ordinate of the position of touch. The circuits are completed as follows. When the X-co-ordinate is being measured the left-hand electrode on the lower layer is connected to ground, the right-hand, electrode on the lower layer is connect to (say) 5 V, and the two electrodes of the upper layer are connected together. The voltage between those two electrodes and ground is then measured. When the screen is touched a voltage will be produced that is somewhere between 0 V and 5 V, depending on the X-co-ordinate of the position of touch. It will be appreciated that the voltage will be independent of the Y-co-ordinate of the touch.
The connections are now altered in order to measure the Y-co-ordinate. The left and right-hand electrodes of the lower layer are now connected together, and a potential difference is applied between the two electrodes of the top layer. The output will of course be the voltage appearing at the combined electrodes of the bottom layer.
The device that applies these voltages and that measures the output voltage when the screen is touched is the so-called controller that was referred to above.
The controller has a further function, namely touch detection. It can be seen that power is consumed continuously while the screen and controller are in the above X-measurement and Y-measurement states. In the X-measurement state, for example, a potential difference is maintained across the lower layer and current will flow whether or not the screen is being touched. The waste of power is considerable since for most of the time the screen will not be being touched. In the touch detection state the controller applies, say, 5 V to both the left and right electrodes on the bottom layer, and connects together the two electrodes of the top layer. No current will flow since there is no potential difference across either of the layers. When the screen is touched the controller detects a voltage at the combined electrodes of the top layer. This causes the controller to re-organise its connections to the screen to apply a potential difference between the left and right electrodes on the bottom layer and make the X-measurement as described above. Once this is done the controller re-organises the connections again to apply a potential difference between the electrodes on the top layer to make the Y-measurement. It may repeat these two measurements one or more times to avoid spurious readings, and then it will return to the touch detection state and await a further touch.
The voltage measurements may be made in any suitable way, but generally an analogue-digital converter (ADC) will be used to produce a digitalized output to be fed to the computer to be controlled by the touchscreen.
A five-wire touchscreen operates in a different, and apparently incompatible, way to that described above. The five wires are connected in the following way. Four of them are connected to the four comers of the lower electrode and the fifth wire is connected to an arbitrary position on the upper electrode. In the touch detection state the four wires to the bottom electrode are connect to, say, 5 V. Detection of a voltage at the top layer indicates that the screen has been touched. This then causes the five-wire controller to switch to its X-measurement state as follows. In this state the top and bottom left-hand comers (again imagine the layer in the vertical plane in front of you) are connected to ground, and the top and bottom right-hand corners are connected to, say, 5 V. Depending on the resistance of the lower layer, the field lines across the lower layer will be considerably curved. A specially designed resistive buss may be provided between adjacent pairs of corners of the lower layer in order to make these field lines more rectilinear. This is disclosed in U.S. Pat. No. 4,661,655 (Gibson et al) the disclosure of which is incorporated herein by reference, and excellent touch screens of this type are marketed by Elo TouchSystems Inc. The nature of any such bussing is not important to the present invention and will not therefore be described further. With the touchscreen and controller in the X-measurement state it can be seen that the voltage appearing on the top layer will be related to the X-co-ordinate of the touch on the screen. Once this measurement has been made the controller and screen switch to the Y-measurement state where the top left and top right corners are connected to, say, 5 V and the bottom left and right corners are connected to ground. Now the voltage on the top layer will give an indication of the Y-co-ordinate of a touch on the screen.
I have discovered that it is possible, and indeed useful, to provide the ability for a five-wire screen to be connected to a four-wire controller, and vice versa. This allows optimum independent selection of screen and controller, and allows part of a system to be upgraded thus avoiding the need for total replacement. Furthermore it makes equipment more compatible with other equipment thus simplifying overall design.
I have found that this can be achieved by providing a converter which can be connected between a screen and a controller, either as an independent piece of equipment or as an add-on to, or as a modification of, either a screen or a controller.
Thus, the present invention provides a converter for connection between an electrographic sensor and an electrographic controller, and comprising:
(a) a first set of contacts for connection to the sensor;
(b) a second set of contacts for connection to the controller; and
(c) an emulator for emulating at the second set of contacts:
(i) a four-wire sensor when the first set of contacts is connected to a five-wire sensor and the second set of contacts is connected to a four-wire controller; and/or
(ii) a five-wire sensor when the first set of contacts is connected to a four-wire sensor and the second set of contacts is connected to a five-wire controller.
In a preferred embodiment both of possibilities (i) and (ii) are provided for. Furthermore, the emulator may additionally emulate at the second contacts:
(iii) a five-wire sensor when the first set of contacts is connected to a five-wire sensor and the second set of contacts is connected to a five-wire controller; and/or
(iv) a four-wire sensor when the first set of contacts is connected to a four-wire sensor and the second set of contacts is connected to a four-wire controller.
Where all these possibilities are provided for the converter will be fully universal, in that either type of sensor may be connected to either type of controller. I prefer that the converter be able automatically to determine which type of sensor and which type of controller are connected to it.
To this end the converter may additionally comprise:
(d) a first device that can determine which of a four- and five-wire sensor is connected to the first set of contacts and/or which of a four- and five-wire controller is connected to the second set of contacts; and which can, at least in part from such determination, cause the emulator to effect an appropriate emulation.
Alternatively or additionally, the converter may comprise:
(e) a second device that can determine which of a sensor and a controller is connected to one of the sets of contacts; and which can, at least in part from such determination, cause the emulator to effect an appropriate emulation.
The risk of connecting the sensor and controller to the wrong sets of contacts can therefore be eliminated.
In general the controller may be provided with two sets of five contacts for example in the form of five-pin plugs and/or five-pin sockets.
The emulation carried out by the converter may consist simply in forming appropriate (direct or indirect) interconnections between the first set of contacts and the second set of contacts. However, in some cases it may be preferred that the emulation consist in reading a signal at a contact of one of the first and second sets of contacts and then writing an appropriate signal to a contact of the other of the first and second sets. This second possibility might be desirable where the sensor requires different voltages or source impedances etc, in addition to different patterns of interconnection, from that provided by the controller.
It was explained above that an electrographic controller passes through several different states, namely touch detection, X-measurement and Y-measurement. In general the converter of the invention will have first, second and third states corresponding to these states of the sensor and controller. Alternatively, a separate converter could be provided for each state and the controller could switch between them. The converter is preferably controlled by the controller and simply follows the changes that occur in the controller. I prefer that the emulator be caused to switch between its states by signals from the controller at the second set of contacts. Thus the standard output (which in the absence of the controller of the invention would be connected directly to the sensor) provides all the information necessary for the controller to change states. An alternative would be to provide some additional connection between controller and converter but this is not at present preferred.
The standard output from the controller preferably also provides all the power necessary for the emulator to effect the appropriate emulation and switching between states. I also prefer that the standard output provide any voltage references needed.
In order to increase reliability of the converter it may be desirable that in the absence of any power the emulator return to its touch detection state. To this end the emulator preferably has switches whose states constitute the state of the emulator, the normal states (ie those states which result from the absence of any applied power and/or the dissipation of any charge) of those switches corresponding to the first, ie touch detection state, of the emulator.
Before a preferred embodiment of the invention is discussed in detail, I will summarise the operation of a fully universal controller of the invention.
On connection of a sensor to one set of contacts and a controller to another set of contacts of the converter, the converter:
(i) determines to which of said sets is connected the sensor and to which of said sets is connected the controller;
(ii) determines whether the sensor is a four-wire sensor or a five-wire sensor;
(ii) determines whether the controller is a four-wire controller or a five-wire controller; and
(iv) causes the emulator to adopt first, second and third states appropriate to the type of sensor and the type of controller connected and according to the state from time to time adopted by the controller.
The controller need not be fully universal in this sense. For example, it could have separate sets of contacts dedicated to the type of equipment to be connected, or it could have switches or other means of control to be operated by the user depending on the type of equipment that is connected.
Where the controller makes the above determinations automatically, a variety of techniques may be used which, in the light of the present specification, the skilled reader will be readily able to devise. For example, the controller may be able to determine whether a sensor or a controller is connected to a given set of contacts by determining whether a voltage exists between any contacts of that set. If a voltage is detected the equipment will be a controller.
Measurement of the resistance between pairs of contacts to which a sensor is detected will determine whether the sensor is a four-wire sensor or a five-wire sensor. Also, a four-wire controller may be distinguished from a five-wire controller by determining voltages between pairs of said contacts.
The controller of the invention may be provided as a separate or free-standing, piece of equipment or it maybe pre-connected to or part of a sensor or pre-connected to or part of a controller.